There have been heretofore many nitride semiconductor light emitting elements, such as LEDs (light emitting diodes) and semiconductor lasers, in which a light emitting element structure including a plurality of nitride semiconductor layers is formed on a substrate of sapphire or the like by epitaxial growth (see Non-Patent Documents 1 and 2 described below, for example). The nitride semiconductor layer is represented by the general formula: Al1-x-yGaxInyN (0≤x≤1, 0≤y≤1, 0≤x+y≤1).
The light emitting structure has a double-hetero structure in which an active layer including a nitride semiconductor layer of single-quantum-well structure (SQW) or multi-quantum-well structure (MQW) is sandwiched between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer. When the active layer is an AlGaN-based semiconductor layer, by adjusting an AlN molar fraction (also called an Al composition ratio), band gap energy can be adjusted within a range where band gap energies that can be taken by GaN and AlN (about 3.4 eV and about 6.2 eV) are lower and upper limits, respectively, so that an ultraviolet light emitting element having a light emission wavelength of about 200 nm to about 365 nm can be obtained. Specifically, when a forward-current flows from the p-type nitride semiconductor layer to the n-type nitride semiconductor layer, light emission corresponding to the band gap energy occurs in the active layer.
On the other hand, in an implementation of the nitride semiconductor ultraviolet light emitting element, flip-chip mounting is generally adopted (see FIG. 4 of Patent Document 1 described below, for example). In the flip-chip mounting, the light emitted from the active layer passes through the AlGaN-based nitride semiconductor and the sapphire substrate having higher bandgap energy than the active layer and is extracted out of the element. Thus, in the flip-chip mounting, the sapphire substrate faces upward, and each of p-side and n-side electrode surfaces formed toward an upper surface side of a chip faces downward, so that the respective electrode surfaces on the chip side are electrically and physically connected to electrode pads on the side of a package component such as a submount through metal bumps formed on the respective electrode surfaces.
In general, as disclosed in FIGS. 4, 6 and 7 in Patent Document 2 or FIGS. 2, 4 and 6 in Patent Document 3 described below, the nitride semiconductor ultraviolet light emitting element is sealed with an ultraviolet light transmitting resin such as a fluorine-based resin or a silicone resin before it is put into practical use. The sealing resin protects an inside ultraviolet light emitting element from an outside atmosphere to prevent degradation of the light emitting element due to ingress of moisture, oxidation and the like. Further, the sealing resin may be provided as a refractive index difference mitigation material for improving light extraction efficiency by mitigating a reflection loss of light resulting from a refractive index difference between a light condensing lens and an ultraviolet light emitting element or a refractive index difference between a space to be irradiated with ultraviolet light and an ultraviolet light emitting element. Further, it is also possible to improve irradiation efficiency by shaping the surface of the sealing resin into a light condensing curved surface such as a spherical surface.